1. Field of the Invention
The invention described herein is directed to supply line filtering for power supplies. More specifically, the present invention compensates for fluctuations in a power supply current caused by time-dependent fluctuation and load current demand.
2. Description of the Prior Art
Although line filtering of supply lines in power distribution systems is well known, it continues to be a field in which beneficial improvements are made. The widespread use of the switching power supplies and electronic circuitry, especially in personal computers, have allowed smaller packaging of systems, but often must be accompanied by supply line filtering to ensure proper operation of the load circuitry.
Of course, not all supply line noise is caused by the supply side circuitry. Time-dependent load demand also introduces a noise component on the supply line, which is typically overcome by adequate regulation of the power supply. Generally, the power regulation is implemented at the power supply using a separate voltage sensing circuit coupled to the load.
In many applications, such as in laser light modulation of optical computing and optical communication, fluctuations in supply current due to changing load conditions present not only power regulation problems, but also considerable security concerns. This is because the modulation of laser light, which forms the transmitted data, may be introduced onto the power supply line as a modulated current. The current modulation may easily be read by an inductive probe coupled to the supply line. This allows a third party to monitor communications which would otherwise be secure.
Prior art line filters which are designed to mitigate amplitude modulation of voltages fail to prevent current modulation of the supply line in systems where the power source has a low internal impedance and where the frequency distribution of the modulation is low. In such systems, current in the supply line can be modulated to a significant degree without a correspondingly significant degree of voltage modulation.
In light of the foregoing discussion of the prior art, there is an apparent need for a current modulation filter for mitigating current fluctuations in a power distribution system.